The present invention is concerned with an insertion-and-withdrawal on ON-LINE status of a printed circuit board loaded with electronic circuits, i.e., with insertion and withdrawal of a printed circuit board to and from a connector without disconnecting an electric source from which the connector is supplied with an electric power.
Systems have been known for performing a transmission of data between a computor and periperal equipments such as input and output means, the input and the output means consist of one or more printed circuit boards each of which being loaded with a concentrated control circuit and connected through a connector, in parallel with each other, to a bus line on a mother board for transmitting the data.
It is a common measure, in these systems, to operate a plurality of printed circuit boards of the input and output means with a single and common power supply. Thus, an insertion or a withdrawal of one printed circuit board, for the purpose of addition or maintenance, inevitably causes a disturbance of signals on the bus line, as well as a fluctuation of the power voltage, which in turn affects badly other printed circuit boards connected to the same bus-line, when the insertion or the withdrawal is made on ON-LINE status, i.e., without disconnecting the power source.
For this reason, conventionally, insertion and withdrawal of a printed circuit board has required to disconnect the power source.
Recent progress of packaging technology has produced highly centralized circuits such as LSI, which in turn affords a system in which a number of input and output means are mounted in a unit and operated with a single and common power source. In order to avoid aformentioned disturbance of signals, it has recently been proposed to provide each circuit board with a disconnecting switch through which the circuit is connected to a common line. However, the addition of switches for the printed circuit boards considerably deteriorates the packaging and mounting technology, and causes an unduly raised cost of production, and, therefore, is almost impracticable.